This application relates to a unique way of maintaining a small amount of lubricant in a scroll compressor slider block/bearing interface to provide short-term lubrication for a compressor during a starved lubrication start-up or operation.
Sealed compressors are part of many refrigerant compression systems. A refrigerant cycle includes a number of elements, and a refrigerant moves between the elements when the cycle is operational. Refrigerant flow lines connect the elements, and the refrigerant flows between the compressor and elements such as the condenser, the evaporator and the expansion valve, etc. At the same time, lubricant may also flow between the several components.
Often at shutdown of the system, the lubricant can drain from one of the components. This becomes particularly acute for the compressor during long periods of shutdown. A refrigerant compressor typically includes a number of inter-engaging or rotating parts which must be supplied with sufficient lubricant to preserve the parts. However, if the lubricant has moved outwardly of the compressor, there may be insufficient lubricant for proper operation of the compressor. Such a xe2x80x9cstarved lubricantxe2x80x9d situation will often occur when the refrigerant cycle has been shut down for a long period of time. At start-up, the refrigerant and the lubricant will again begin to flow between the various element of the cycle, and after a short period of time the lubricant will return to the compressor housing. However, in the past, compressors have sometimes been damaged during this start-up time. Other events occurring during operation of the refrigerant cycle may also cause momentary loss of oil supply at the compressor.
One type of modern refrigerant compressor is a scroll compressor. In a scroll compressor, a pair of scroll members each include a base and a generally spiral wrap extending from the base. The wraps interfit to define compression chambers. One of the two scroll members is caused to orbit relative to the other. Typically, a shaft is driven by a motor and has an eccentric extending upwardly into a slider block. The slider block is mounted within a bearing in the orbiting scroll member. There is a loaded and unloaded position between the eccentric and the slider block. The force transmitted between the eccentric and the slider block at the loaded position may be substantial, and during operation of a scroll compressor it is important to have a film of lubricant between the slider block and its bearing.
However, during the starved lubricant conditions mentioned above, there is no lubricant, and damage can quickly occur.
In a disclosed embodiment of this invention, the drive interface between a rotating shaft and a compressor pump unit element is provided with a lubricant retention feature. More preferably, the drive interface is between the slider block and the bearing in a scroll compressor. In the inventive preferred embodiment, oil retention grooves are formed in the outer periphery of the slider block. The oil retention grooves are structured such that they will not drain to the sump at shutdown or during a loss of oil supply during operation. That is, the grooves extend into the surface of the slider block, but do not communicate to an end of the slider block.
Preferably, the retention grooves are greater than the oil film thickness by an order of magnitude. In this way, oil is retained in the grooves such that there will be sufficient lubricant to form a thin lubricant film between the slider block and the bearing during oilstarved operation or at start-up should start-up occur in an otherwise xe2x80x9cstarvedxe2x80x9d lubricant condition. To that end, the grooves preferably have a depth between 200 microns to three millimeters. The term xe2x80x9cgroovesxe2x80x9d is used in this application to include any structure or recess formed into the outer peripheral surface of the slider block. In preferred embodiments there are actually a plurality of indentations having a diameter on the order of two millimeters. However, grooves extending circumferentially or axially, and not extending to the ends of the bearing may also be utilized.
More preferably, the grooves are formed at a circumferential extent spaced from the area or position of load transmission between the slider block and bearing at a loaded condition. At the loaded position there is a very thin film of very high pressure oil between the slider block and bearing during full operation of the scroll compressor. Forming the indentations at a location spaced from this loaded position will ensure that the indentations will not disrupt any creation of the oil film in the critical loaded position of the slider block during normal operation of the compressor.
In sum, recesses are formed in an outer periphery of the slider block of a scroll compressor. The recesses maintain a quantity of oil even after a long period of shutdown. At start-up, or in an otherwise starved lubricant condition, the recesses supply lubricant to the interface between the slider block and the orbiting scroll bearing. This lubricant allows the scroll compressor to operate without damage for a period of several minutes. This time should be sufficient for the entire refrigerant charge to recycle through the system to return lubricant to the compressor.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.